A standard utility knife of the type used for deburring plastic castings has a grip-shaped handle whose front end is provided with a removable steel blade. The rear end of the handle is rounded to fit comfortably in the hand, and the middle region is provided with grip-enhancing formations. In the system described in commonly owned German patent 4,112,482 filed Apr. 17, 1991 by E. Beermann the handle is adjustable with respect to length. To this end its rear portion is formed by a cup-shaped or tubular handle that fits over and is threaded to a stem projecting backward from the front and middle parts of the knife body. Thus this rear handle portion can be screwed on the stem to increase and decrease the length of the knife.
While this arrangement does have the considerable advantage that it allows the knife to be adjusted to fit the user's hand, it has several disadvantages. In order to change the handle length over a wide range, for instance from very short to very long, one must laboriously screw the handle part the whole length of the stem because the pitch of the screwthread is fairly shallow to prevent the handle from screwing in when pushed forward during use. Furthermore assembly of the tool requires a laborious screwing of the handle onto the body, increasing production costs. Once in use it is possible to accidentally screw the handle back off the body, separating the parts so that the real possibility of losing the handle is created.